Rashi on Deuteronomy 7:12/רש"י על דברים ז׳:י״ב

1והיה עקב תשמעון AND THE CONSEQUENCE WILL BE, IF YE HEARKEN (The Hebrew text may be taken to signify if you will hear the heel, עקב) — If, even the lighter commands which a person usually treads on with his heels (i.e. which a person is inclined to treat lightly), ye will hearken to,

2ושמר ה׳ וגו׳ THEN THE LORD [THY GOD] WILL KEEP FOR THEE His promise (Midrash Tanchuma, Eikev 1).